Diaphragm for telephone instruments



DC. ZS 1928.

1,696,807 E. V. MACKINTOSH ET Al.

Dummy! FOR TELEPHONE INSTRUMENTS Filed Aug. is, 192e f. vv:YA: A Y Y f Y Y Y Y Y A.

/A/vs/vTa/es f.' 1./ /Vdcr//v Tas/y C? '/vc Patented Dec. 25, 1928-.

UNITED STATES 1,696,807 PATENT oFFlcE.

ERIC VINCENT IACKINTOSH, F NEW IALDEN, AND'C'YBIL FRENCH, 0F HAMPTON WICK, KINGSTON-ON-THAIES, ENGLAND.

DIAPHRAGI FOR TELEPHONE UUSTBUIENTS.

Application led August 13, 1928, Serial No. 129,015, andvin Great Britain October 24, 1925.

This invention relates to improvements in dia hragms more particularly for use in lou -speakers and of the kind having an areamany times greater than that of eartelephone diaphragms or those commonly medium for transferring the movements ofa vibratory member to the air, in the form of sound waves. The extent to which this is achieved is mainly dependent on the area., of such a surface, that can be made to follow the movements of the vibratory member.

This area, in the case of a diaphragm actulated at a single point, such as the centre, at any particular frequency, is, in turn, dependent upon the mass and rigidity of the diap ,and the manner in which it is The effective area of a 'diaphragm may be increased, either or both, by reducing its mass or b increasing its rigidity, and this area will he greatest at the lowest frequencies.

The actual dimensions of a diaphragm required to respond to frequencies over the whole audible ran e will be governed mainl b the area whic 4u ectively at the lowest frequencies, as there will be no advantage in exceeding this area, and any reduction of area will impair the eciencyof the diaphragm at the lower frequencieahr h A dia a a a large effective area will belinorndr levjssnlamped accordm' g to the extent of this area, with consequent broadening of its natural resonance characteristic. Hence we find that increasing the eiective area not only increases the eiliciency, but, by damping out natural resonance, the response throughout the whole ange of frequencies is rendered more uniorm..

'at its centre.

' In accordance, then, with our Istatement that the volume eiiiclency and the evenness -of .response throughout the scale are both mainly determined bythe eilective area of a diaphragm, which is, in turn, dependent on the rigidity and mass of the diaphragm, and the manner inwhich .it is mounted, we have devised means for carrying these conditions into effect to the bestadvantage.

We employ a diaphragm of conical form and mount it by clamping it rigidly around its edge, to provide a larger effective vibratsheet material only were used. We can make i our diaphragms of a diameter as large as twelve inches, the whole area of which will be effective at the lowest frequencies, though the weight can be less than one ounce.

The natural period of this size or diaphragm is of the order of 60 vibrations er second whichis sufficiently low to give e ec- The edge of the diaphragm may be he orclamped in any known or convenient nuan-A ner, but in one form the edge is attached by glueing to an annular eof some stiff material, such as Bristol board, 'of the same tive response down to the limit of audibilitly.

diameter as the diaphragm, which may form part oftheconv taining case, and will screen The annular' frame may he used without an external case and would then be made of suiciently strong material.- The diaphragm is attached to the amature or driving ve will now our invention with re erenoe to e accompanying drawing which is largely di atie, with the cas ainsectlon. The ntofthecaseisopen at b and may have therein an ornamental fret or equivalent as indicated by c.

The diaphragm 1 is of conical form and is 'ohnnectedaftttithereedorrmature.

e edgle o e aphragm is ed at l to a cylin er of cardboard or other material 4monntedontheback5of thecasea'so y one side of the diaphragm from the other. can be made to vibrate thatthe said back with the cylinder, diaphragm and magnet system can be removed en bloc from the case.

Reinforcing strips are indicated at 6 and are Afor example madeof thin strips of cane. The case may be formed as a cylinder or be of any appropriate shape.

The drawing shows a construction in which the diaphragm is fixed all round its edge to the cylinder 4 and whilst this form is generally preferable, it may be fixed at intervals, if desired, and any clamping or other fixed means, detachable or permanent, which will affect the natural period of vibration of the diaphragm to an extent similar to that of clamping rigidly all round, may be employed.

The word conical herein employed includes modifications of a true cone in that, for example the point may be' fiat or the sides may he or may contain flat parts so.

that in cross section the cone would not be a true circle.

What we claim is:

1.A' loudspeaker comprising a case, a cylindrical frame located within the case and secured at the inner edge thereto, anda conical diaphragm having a maximum diameter corresponding to the diameter of the frame, the outer edge of the diaphragm being secured to the outer edge of the frameV and the apex of the diaphragm extending inwardly of the frame;

2. A loud speaker comprising a case, a cylindrical frame secured at one edge to the case, a conical diaphr having a maximum diameter corresponding to the diameter of the frame, the outer edge of the diaphragm being secured to the outer edge of the frame Y and the apex of the diaphragm extending in.

In testimony whereof we aix our signa-v tures. v

ERIC VINCENT MACKINTOSH. CYRIL FRENCH. 

